Embodiments described herein generally relate to the production of glass cloth for use in printed circuit boards.
Printed circuit boards are typically formed from laminated layers of fabric composed of reinforcing fibers, such as glass fibers. The reinforcing fibers provide dimensional stability to the board to maintain the integrity of the electronic circuits mounted thereon. Holes are formed in the board by drilling through the layers of the laminate or support to interconnect circuits through different planes.
Manufacturing of glass fibers that are used in printed circuit boards require many steps prior to the use of the fabric within laminates. In the first step, molten glass is extruded through holes to produce the glass fibers. Next, the fibers pass through a zone where a sizing material, such as a starch-oil emulsion, is added to the individual fibers. The sizing material is needed as it protects the fibers from abrasion and prevents surface defects. Then, the fibers are formed together to create strands of glass fiber that is then wound onto spools. After spooling, the strands are then woven to generate the glass cloth.
In the case of composites or laminates formed from fiber strands woven into fabrics, in addition to providing good wet-through and good wet-out properties of the strands, the surfaces of the fiber strands are then coated to protect the fibers from abrasion during processing, provide for good weavability, particularly on air-jet looms and preventing damage to the fibers during the weaving process. However, many sizing components are not compatible with the resin and can adversely affect adhesion between the glass fibers and the polymeric matrix material. For example, the starch-oil emulsion, which is a commonly used sizing component for glass fibers, is generally not compatible with resin. As a result, these incompatible materials must be removed from the fabric prior to impregnation with the resin.
The removal of such non-resin compatible sizing materials (also referred to as de-greasing or de-oiling the fabric) can be accomplished through a variety of techniques. The removal of these non-resin compatible sizing materials is most commonly accomplished by exposing the woven fabric to elevated temperatures for extended periods of time to thermally decompose the sizing materials (commonly referred to as “heat-cleaning”). A conventional heat-cleaning process involves heating the fabric at 380° C. for 60-80 hours. However, such heat cleaning steps are detrimental to the strength of the glass fibers, are not always completely successful in removing the incompatible materials and can further contaminate the fabric with sizing decomposition products. Other methods of removing sizing materials are available, such as water washing and/or chemical removal. However, such methods generally require significant reformulation of the sizing compositions for compatibility with such water washing and/or chemical removal operations and are generally not as effective as heat-cleaning in removing all the incompatible sizing materials. Further, heat-cleaning, water washing or chemical removal operations all add to the cost of production as well as the time expenditure.
After weaving, the fabric must be modified to allow the cloth to bond with the resin used in the lamination step to produce printed circuit boards. A silane modifier is used to treat the fabric. On one end of the silane modifier is a functionality for bonding the fibers within the fabric. On the other end of the silane modifier is a functionality for bonding to the resin material. This enhances the adhesion between the cloth and the resin. The now treated glass cloth can be impregnated with resin and then used to form the laminate.
As such, there is a continuing need in the art for methods and systems for glass fiber printed circuit board manufacture which reduce cost of production while maintaining or increasing resulting quality.